Impact of reflection on the fluence rate distribution in a UV reactor with various inner walls as measured using a micro-fluorescent silica detector.

An assessment of the impact of ultraviolet (UV) reflection from inner walls is important for the accuracy of model predictions of fluence rate (FR) distribution and for the improvement of reactor efficiency. In this study, the FR distribution in an annular UV reactor with inner walls of various reflectances was measured in-situ by using a 360° response micro-fluorescent silica detector. The tests were performed in water with various transmittances ranging from 65% to 99% and with inner reactor walls composed of quartz/aluminum foil, quartz/stainless steel, or quartz/black cloth, whose reflection coefficients were determined to be 80.5%, 26.1% and 11.1%, respectively. The results demonstrate that an inner wall with a high reflection coefficient can lead to a marked increase in the weighted average FRs, thus greatly improving the reactor efficiency. Furthermore, the presently used FR distribution models could have an error of up to 35% for commonly used stainless steel walls as a result of the influence of inner-wall reflection. Finally, it was found that the uniformity of the FR distribution is strongly dependent on the diffuse reflection property of the inner wall, which could lead to a better fluence delivery distribution in the UV reactor. This work has potential application to increase the accuracy of model predictions as well as optimize the design of high-efficiency UV reactors.